The invention will be described in the context of an Automatic Vehicle Identification (AVI) system capable of exchanging data codes between an interrogator and a transponder. The AVI field is but one environment in which the inventive concepts described herein can be applied. Systems using batteryless transponders, as well as transponders with batteries, may be used for identifying or locating objects bearing the transponders such as cattle, luggage or other items.
With respect to AVI systems, generally, the interrogator is provided in a toll booth of a toll road, parking garage or other limited access facility. The interrogator (reader) identifies passing automobiles by sending wireless interrogation signals to a transponder (tag), which would normally be a small, self-contained unit placed, for example, on the dashboard or windshield of the car. In this way the car (or other vehicle or object) can be identified in a speedy and efficient manner. Depending on the use of the system, an account associated with the driver, owner, or other designated person can be debited with an access charge. Compatibility standards for one such AVI system are set out in Title 21, Division 2, Chapter 16, Articles 1-4 of the California Code of Regulations, herein known as the Caltrans specification or Caltrans spec. The AVI equipment for toll collection typically consists of two functional elements: vehicle-mounted transponders and fixed-position interrogators.
In prior art applications there have been so-called "money on the tag" applications. In these applications the user would take his transponder to a toll agency where special equipment could program data, representing a certain amount of money, into the transponder. The main disadvantage to this prior art application is the loss of privacy in that the user would have to take his transponder to another person, that person typically being the tollway agent. See e.g., U.S. Pat. No. 5,144,533 to Hassett et al. This prior art application also has a substantial disadvantage in that it does not provide the convenience of the smartcard.
Within the prior art of payment systems, it is known to use "smartcards" for exchanges of goods and services. Smartcards are generally about the size of a credit card and have a microprocessor embedded in them. The smartcard can generally read, write and store information. In a typical application, the user will access an automated machine through which data representing an amount of money may be written into the smartcard memory. Each time a good or service is purchased using the smartcard, the data in the smartcard memory is debited to reflect the amount of the transaction. An advantage of using smartcards, in addition to potential increases in user privacy, is the potential to eliminate point-of-sale equipment. Smartcards have been implemented, or are anticipated to be implemented, in numerous applications: pay phones, automated banking, automated vending and the like. Automated machines for storing data in smartcards might be placed in post offices or stores.
In prior art AVI applications using smartcards, dual gantry systems are used. In the dual gantry system the transponder smartcard access is begun at a first gantry. Because of the slowness of the transponder smartcard interface the transaction must be completed at a later gantry. The disadvantages of such a prior system is the cost associated with construction of multiple gantries per toll plaza. Another disadvantage of such a system is the complexity of coordinating actions between the first gantry and the later gantry.